(1) Field of the Invention
The present invention relates to a pivot shaft structure for scissor mechanisms and more particularly to a cam-like shaft structure for a scissor mechanism to limit the moving angle of the scissor mechanism.
(2) Description of the Prior Art
Among free elevation mechanisms, scissor mechanisms are widely used to support all kinds of loading, whether light or heavy loads. For instance, they can be used in heavy-duty applications such as uplift elevators, cranes and the like. The light-duty applications can be seen in keyswitchs for notebook computers, scissor extension mechanisms and the like. FIG. 1 illustrates a scissor mechanism 12 adapted for a keyswitch 1 of a notebook computer keyboard. The scissor mechanism 12 has a dual-linkage structure located between a key cap 11 of the keyswitch 1 and the base plate 10 of the keyboard. In the actual embodiments implemented in the notebook computers, an elastic rubber dome 13 for providing resilience force to the keyswitch is disposed between the key cap 11 and base plate 11, and the keyswitch is also disposed between the two dual linkages.
As shown in FIG. 1, the scissor mechanism 12 has two bars 121a, 121b located at either side. The two bars 121a, 121b are crossed at a middle portion and engaged by a pivot shaft structure 120. Referring to FIG. 2, the pivot shaft structure 120 consists of a round shaft 122 located on one bar 121b and a mating round aperture 123 formed at another bar 121a. The round shaft 122 is rotatable in the round aperture 123 thereby to allow the two bars 121a, 121b of the scissor mechanism 12 to perform lifting and lowering operations.
In the conventional scissor mechanism 12 with dual symmetric linkage bars (especially those of smaller sizes), the linkage bars at two sides are moving synchronously. In order to make production easier and to coordinate the movements, the bars 121a, 121b of the two linkage bars are usually integrally made and formed. The integral form may be a rectangular frame or an U-shape. For instance, in the scissor mechanism 12 shown in FIG. 1, two pairs of corresponding bars 121a, 121b are respectively formed in a rectangular frame and an U-shape (shown by broken lines for the portions hidden below the key cap 11).
In the conventional scissor mechanism 12, the round shaft 122 may turn freely in the round aperture 123. Hence, it takes great care to install the scissor mechanism 12 on the applied device (there are four installation points located up and down at one side of the scissor mechanism 12). It is important in the art that special attention is required to install the scissor mechanism 12 at the correct direction, for installing the scissor mechanism 12 at the wrong position will affect subsequent assembly and operations. The concern of installation direction is particularly obvious and keen for the smaller size scissor mechanisms used in the keyboards.
One of the shortcomings of the scissor mechanism 12 that the two bars 121a, 121b have to be assembled in advance. As the round shaft 122 may turn freely in the round aperture 123, under certain circumstances it could happen that the round shaft 122 supposed to be assembled and installed for turning purpose will be mistakenly installed as a slide shaft (for instance, being mounted at the locations on the base plate 10 for supporting the two bars 121a, 121b). Namely, the two bars 121a, 121b are turned mistakenly for 180 degrees before the scissor mechanism 12 is installed. As a result, the subsequent assembly work and operations will have serious problems. This type of problems cannot be totally avoided even for the integrally formed bars 121a, 121b (as shown in FIG. 1), because to recognize the correct direction for the rectangular frame is difficult.
Taking the keyboards of notebook computers for example, when the scissor mechanism 12 is installed at the wrong direction, the keyswitchs of the mistaken keyboard will have an abnormal height and their depressing operation will also be affected. Hence, in the industry, in order to achieve correct installation, the correct direction will be usually labeled or marked on the scissor mechanism. Whereas, for the scissor mechanisms of smaller size, the space and size for attaching the labels or marks is limited. Even with the labels or marks attached, their sizes will be definite too small to be recognized. Moreover, because the scissor mechanisms used in the notebook computers are tiny, errors of installation direction are usually difficult to be aware from their appearances. Hence, to distinguish the correct installation direction becomes a process bottleneck in the installation of the scissor mechanism.
The limited sizes of width and thickness of the bars 121a, 121b is another drawback of the conventional scissor mechanism 12. The round aperture 123 formed in the bar 121a will result in a very thin structure for the bar 121a around the round aperture 123 and thus severely weakens the structural strength of the bars 121a, 121b. 